The Holocene biogeography of Pinus sabiniana Douglas ex D. Don (gray pine) in California

Pinus sabiniana Douglas ex D. Don (gray pine) is one of the dominant species in the ubiquitous Gray Pine-Blue Oak Woodland that rings the Great Central Valley of California. The species is absent, however, in a nearly 100 km section of the Sierra Nevada foothills between the Kings and Kaweah rivers. We test several previous explanations for this biogeographic gap, including prehistoric and historic anthropogenic burning, Early Holocene pluvial lakes as a migration barrier, and unique topography as a limiting factor. Through the examination of archaeobotanical and radiocarbon evidence, we find that gray pine distribution has been stable for the past 4,000 years and likely longer. Importantly, gray pine is absent in 44 of 45 individual samples from the Wahtoke Creek Site, the only archaeological site with archaeobotanical data within the modern distribution gap. This suggests that gray pine has been largely absent from the gap for over 6,000 years and refutes several previous explanations for the biogeographical gap. Instead, data support a topographical or ecological peculiarity of the gap rather than historic or prehistoric anthropogenic burning, or an Early Holocene migration of the species that was blocked by bodies of water in the Central Valley.